Why did hundreds of salmon suddenly die in Alaska?

A tourist filmed hundreds of dead salmon in this river in Alaska. (Screen grab of the video by Ales Richter)
A tourist filmed hundreds of dead salmon in this river in Alaska. (Screen grab of the video by Ales Richter)

A tourist visiting Alaska posted a haunting video on August 6 showing scores of dead salmon floating in the waters of Tutka Bay Lagoon. The FRANCE 24 Observers team decided to find out what was the cause -- and why other many other salmon die-offs have been reported across the state.

While out kayaking, Ales Richter, a Czech tourist on vacation in Alaska, captured a 13-second video showing hundreds of dead fish in the Tutka Bay Lagoon in the southern part of the state. When he posted the video to Facebook, Richter blamed “the incredibly warm and sunny summer” and generally rising temperatures due to global warming for the deaths of fish.

Richter’s video garnered more than six million views on Facebook and was reposted on several other pages -- each time with the same explanation -- that global warming was the culprit. In August, the temperature in Tutka rose to 23 degrees Celsius. At the same time last year, the temperature in Tutka was lower -- between 16 and 19 degrees Celsius.


However, according to local media, these fish deaths were the result of an accident, not global warming. The FRANCE 24 Observers team spoke to Dean Day, the executive director of the Cook Inlet Aquaculture Association, which works on salmon conservation and runs a hatchery in Tutka Bay Lagoon. Members of thIS association occasionally fish in the lagoon to finance their activities, using a net called a seine that hangs vertically in the water with its bottom edge held down by weights and its top edge buoyed by floats.

This unfortunate incident happened on July 28 while we were fishing. Our seiner [a type of net] broke after snagging on something in the water and many salmon were trapped in the net, crowded into a very small space. Quite a few of them died from shock and lack of oxygen and, when the net eventually tore open, their carcasses floated to the surface. We estimate that about 1,200 salmon died in the accident. Overall, however, we were able to harvest more than 13,000 living salmon [and sell them to a processor]. As far as I know, aside from this accident, there weren’t any other unusual fish deaths in the region.

This account was confirmed by Glenn Hollowell, the local management biologist with the Alaska Department of Fish and Game, who works specifically on salmon. Hollowell told local media outlet the Homer News that he had seen Richter’s video and that he definitely didn’t think that warm temperatures were to blame for the fish deaths, as the tourist who made the video claimed.

“It would be unusual that the fish would be grouped that tightly in the same direction,” Hollowell said. “They were all similar quality. They were all similar fish.”

Salmon deaths across Alaska

However, over the past few weeks, other Alaskans have also reported suspicious salmon deaths in their areas. Reports have come in from all different parts of the state, which extends over 1.718 million kilometers - more than twice the size of France.

Female salmon die off naturally about two months after spawning, sometime between June and August. However, this summer, local activists and researchers have found quite a few dead female salmon who were still carrying healthy eggs.

Ricko de Wilde lives in Husila, on the shores of the Kokuyuk River. De Wilde also took to Facebook to post about curious salmon deaths in his area -- which is close to 720 kilometers from Tutka Bay where the fishing accident took place.

On June 20, De Wilde posted his concerns on Facebook.

I just drove 200+ miles on it and literally seen them floating everywhere. We just had weeks of 80 degree weather [equivalent to about 26 degrees Celsius] so it may be [heatstroke]. It would be good to have the [F]eds send out some scientists to look into this matter because the way it’s looking we may be seeing a very low return of salmon for our future generations.

At this time last year, the average temperature in Koyukuk was just over 16 degrees Celsius.

De Wilde isn’t the only person to notice exceptional numbers of salmon dying. People all across Alaska -- from Kuskokwim to Norton Sound to Bristol Bay -- have all reported similar worrying sightings, as you can see in the map below.

"Tens of thousands of fish have died from heat across Alaska"

Doctor Stephanie Quinn-Davidson, who directs the Yukon River Inter-Tribal Fish Commission, conducted a study looking into salmon deaths along a 200-kilometre of the Koyukuk River.

All signs point to heat as the cause for this salmon die-off in the tributaries to the Yukon River.

We examined the dead salmon for any indications of disease, parasites, infections, tumors - or anything else that would have indicated they were sick. We ruled out pollution because this area is pristine, nor does it have wastewater discharges.

By all indications, these salmon looked perfectly healthy, but they just hadn't spawned yet and didn’t seem close to doing so.

We had about four or five days of extreme heat in Alaska between July 7 and 11 when air temperatures were about 20 degrees [Fahrenheit, equivalent to 7 degrees Celsius ] above average. Locals told us that they started seeing dead salmon on July 12.

We also experienced low water levels in many areas, which would have made it difficult for the salmon to find refuge in deeper, cooler pools.

The die-off seemed to peak a week or two later, when we started getting more reports from locals.

As soon as the temperatures cooled back down, we stopped seeing dead salmon. The fact that we saw this across Western Alaska river systems around the same time makes us fairly confident this was all related to the heat.

It's very likely the numbers of dead salmon are in the thousands, and quite possibly in the tens of thousands. And this is just the Yukon River. Salmon die-offs have been reported on the Kuskokwim River and Bristol Bay. I have a friend who fishes in Ugashik Bay and she counted over 500 dead salmon within one mile of her fish camp. She has fished there for over 30 years and has never seen anything like it.

According to local media in Alaska, record water temperatures were recorded across the state. Stream temperatures near Anchorage 24.4 degrees Celsius for the first time since 2002.


Article by Ershad Alijani (@ErshadAlijani).